Day of the Week Finder

Day of the week finder

Find out which day of the week any date falls on — past or future. It answers everyday questions like “what day was I born?”, “what weekday does my flight land?”, “does that bank holiday fall on a Monday?” or “is that project deadline a weekend?” in one click.

How it works

You pick a date and the tool reads its weekday from the JavaScript Date object. Internally, days are numbered 0 for Sunday through 6 for Saturday. The finder converts that raw index into three pieces of information:

• The named weekday formatted in your browser’s locale — so a French browser may display “lundi” while an English one shows “Monday”
• The ISO 8601 weekday number, which runs Monday = 1 through Sunday = 7, matching the convention used in spreadsheets, databases, and the ISO week system
• A weekend flag indicating whether the date falls on Saturday or Sunday (the common Western definition) or is a regular weekday

Because the date is treated as a pure calendar date with no time component, the result is the same in every time zone.

Why ISO weekday numbers matter

Most programming languages and spreadsheet functions use the ISO convention (Monday = 1 … Sunday = 7) or a variant of it (Sunday = 0). Knowing the ISO number for a date lets you write date logic like “process only if weekday <= 5” without converting day names to numbers yourself. The ISO number is also the basis for calculating which ISO week number a date falls in.

Historical and future dates

The tool works equally well for dates centuries in the past or the near future, within the range a browser date object can represent. For example, 1 January 1900 was a Monday, and the formula handles the Gregorian calendar change correctly for dates within the modern calendar system.

Quick reference — recent and upcoming dates

Everything runs entirely in your browser — your date is never uploaded anywhere.